Multi-channel, high gain linear amplifiers for transmitters are described, for example, in the above cross-referenced patent application corresponding to German Patent Publication P 3,733,374. Such amplifiers require a network which provides a drive control signal with the appropriate amplitude and phase characteristics for each individual channel. The amplifier channels require different input signals dependent on the momentary modulation signal. Therefore, the network must realize a nonlinear transfer function. Moreover, the network must have a sufficient broadband characteristic so that the band width of the entire system is not limited by the network. Furthermore, the losses in the network should not be too large. The feedback due to dynamic matching variations should be small, and costs should be as low as possible. There is room for improvement in these respects.
Previously, multi-channel transmitters have been realized only in conjunction with modulated transmitter amplifiers as described, for example,in H. Chireix High Power Outphasing Modulation Proc. I.R.E., Volume 23, No. 11, (November, 1935), pages 1370-1392, and W. H. Doherty: "A New High Efficiency Power Amplifier for Modulated Waves", Proc. I.R.E., Volume 24, No. 9, (September, 1936), pages 1163-1182. In connection with such modulated amplifiers, the envelope curve of the modulated signal is explicitly at hand, so that it is immediately possible to realize the necessary control voltages as a function of the envelope curve using suitable circuit components, for example, capacitive diodes. However, the conventional method cannot be used for broadband linear amplifiers because the envelope curve signal has a band width which is a multiple of the amplifier band width. Thus, in that case, an explicit processing of the envelope curve would unallowably limit the band width of the amplifier.
This problem led, early on, to attempts to solve it by synthesizing the drive control voltages without manipulating the envelope curve signal. The only known successful solution to that problem is described by J. Fagot and H. Chireix (French Radio Electric Society) German Patent (DRP) 759,851, Dec. 3, 1939. The described solution uses a high frequency (HF) negative feedback path for generating the drive control voltages.
However, in the typical modern multi-stage semiconductor amplifiers or in high gain microwave tubes, the known method is not practical because the transit time in the amplifiers leads to instabilities. Besides, the known method achieves an insufficient band width.